This invention relates generally to lubricant compositions capable of operating at high temperatures and, more particularly to a polyol ester lubricant composition suitable for use as a chain and drive gear lubricant operating at temperatures in excess of 250xc2x0 C.
There are continuing demands for lubricant compositions suitable to operate at high temperature in excess of 250xc2x0 C. Such lubricants must provide lubrication and antiwear protection. In addition, they must be stable in the high temperature environment, or decompose harmlessly without forming hard, varnish-like deposits or unacceptable amounts of smoke. Many industrial processes involve operation of open chain and drive gear assemblies that are associated with ovens, furnaces, kilns and other hot equipment. Such chain and drive gear assemblies are used in the manufacture of textiles, wallboard, corrugated metal, paper and plastic film.
In addition to not forming deposits or varnish and possessing stability at high temperatures, the lubricants must perform under high load, be compatible with all materials in contact with the lubricant and be low in volatility. Existing commercial lubricants for chain and drive gear operations, which are based on vegetable oils or other glycerol-based esters and mineral oil, lack sufficient high-temperature stability. Polyolefins or polyacid esters also lack the necessary high-temperature stability. All these lubricants are prone to varnish formation and are characterized by relatively high volatility, as well as severe compatibility problems with silicone elastomers.
In industrial chain and drive gear assemblies operating in a static mode, spent lubricant collects and remains in pools under high temperature conditions. This causes the lubricants to form varnish-like deposits that are highly undesirable. Such deposits often lead to equipment failure, increased down time and higher maintenance costs. Varnish formation results primarily from thermal and oxidative degradation as well as by excessive evaporation.
One such high temperature chain and drive gear lubricant is described in U.S. Pat. No. 5,151,205 to Calpon, Jr. While the Calpon patent describes a wide variety of synthetic polyalphaolefin based oils and ester based oils, the described compositions include a polyalphaolefin base oil, an ester oil solubulizer and 2-4 weight % of a polybutene tackifier. The composition is promoted for reducing smoking in chain and drive gear assemblies operated at high temperatures. However, as shown in comparative testing below such lubricants based on these polyalphaolefins tend to evaporate under high temperature exposure and are not fully satisfactory. Presently, no 100% polyol ester based chain lubricants are fully satisfactory in this respect.
Accordingly, it is highly desirable to provide high temperature lubricants suitable for use in high temperature chain oil environments that exhibit reduced evaporation rates under high temperature conditions and avoid the varnish/deposits shortcomings of the commercially available chain oil lubricants.
Generally speaking, in accordance with the invention, improved synthetic lubricants based on a 100% polyol ester composition suitable for use in high temperature static chain oil applications is provided. The lubricant includes a base stock based on a polyol ester that is the reaction product of a neopentyl polyol including a major proportion of dipentaerythritol and a mixture of C5 to C12 carboxylic acids. The preferred acid mixtures include heptanoic (C7) acid, caprylic/capric (C8-10) acid and isononanoic (3, 5, 5-trimethylhexanoic) acids (iso-C9). The polyol ester composition should have a molecular weight average of at least about 750. It includes a major proportion of polyol esters with neoalkoxy structural elements, specifically with no beta hydrogen on the polyol moiety that precludes thermal degradation to an olefin and carboxylic acid. The viscosity of the polyol ester should be at least about 100 to 125 cSt at 40xc2x0 C.
The polyol ester base stock is mixed with viscosity index improver (tackifer) and an additive package that includes antioxidants, extreme pressure/anti-wear agents and a corrosion inhibitor. The additive package may be added in up to about 20 percent by weight of the lubricant to provide a viscosity of the lubricant at 40xc2x0 C. of at least about 275 cSt and at 100xc2x0 C. of no less than about 25.0 cSt. When placed in a circulating air oven at 230xc2x0 C. for 80 hours, the formulated lubricant will have a percent weight loss less than about 20 weight %.
Accordingly, it is an object of the invention to provide a synthetic ester lubricant suitable for use in high temperature chain oil applications.
Another object of the invention is to provide an improved synthetic ester lubricant including a major proportion of polyol esters lacking a beta hydrogen suitable for use in high temperature chain oil applications.
A further object of the invention is to provide an improved polyol ester lubricant including a viscosity index improver (tackifer) and an additive package that includes antioxidants extreme pressure/anti-wear agents and corrosion inhibitors.
Yet another object of the invention is to provide an improved high temperature polyol ester synthetic lubricant including a major proportion of dipentaerythritol esters and an additive package that has reduced weight loss when subject to heat for extended periods of time.
Still another object of the invention is to provide an improved polyol ester lubricant for high temperature application that does not form hard varnish and undesirable deposits when subject to high temperature.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.
The invention accordingly comprises a composition of matter possessing the characteristics, properties and the relation of components that will be exemplified in the compositions hereinafter described, and the scope of the invention will be indicated in the claims.